THUNDERSTORM CHARACTERISTICS OF IMPORTANCE TO WIND ENGINEERING
Franklin T. Lombardo
Thunderstorms dominate the extreme wind climate in most of the United States at mean recurrence intervals (MRI) that are important for design wind loading. Although thunderstorms are important for wind loading, a lack of full-scale thunderstorm data has been collected and analyzed. Therefore, design criteria in the US wind load standard (ASCE 7) are based on a) data without explicit consideration for thunderstorms and b) wind tunnel and full-scale data that exhibit stationary properties (i.e. unchanged over some time period). These stationary properties are usually not characteristic of full-scale thunderstorm events, especially those accompanied by wind speed increases occurring over relatively short time scales (i.e., “ramp-up” events). In addition, the physical characteristics (e.g. vertical profiles, turbulence) of thunderstorm winds have been shown to be somewhat different than that of the wind data used to develop ASCE 7.
As additional full-scale thunderstorm wind data has become available, it is becoming realistic to perform detailed analysis of thunderstorm wind data, make sound comparisions with stationary wind data, and to propose the inclusion of thunderstorm criteria in future versions of ASCE 7. High resolution, full-scale wind data from thunderstorms, including ramp-up events were collected at Texas Tech University and from archived data via the Automated Surface Observing System (ASOS). Parameters important to wind loading such as wind velocity at specified MRI, vertical wind profiles, turbulence and pressure coefficient were estimated from the thunderstorm wind data and compared to parameters generated from full-scale stationary wind data and parameters already in place in ASCE 7.